Aircraft engine gearing



June 6, 1944. J TJAARDA 2,350,377

AIRCRAFT ENGINE GEARING Filed July' s, 1940 4 Sheets-Sheet 2 ATTORNEY- Patented June 6, 1

UNITE AKRCRAF'E ENGKNE GEARING John Tjaarda, Detroit, Mich, assignor to Briggs ufacturing Company, Detroit, Mich, a corporation of Michigan Application July 3, 1M4), Serial No. $3,841.

9 Claims.

This invention relates to aircraft and more particularly to the power plant thereof and the drive mechanism for rotating the propeller shaft of the aircraft from the crankshafts. In accordance with one phase of the invention the power plant or engine is of the internal combustion type embodying a number of banks of cylinders having reciprocable pistons for driving a plurality, such as two, parallel crankshafts which in turn drive a propeller shaft.

An object of the invention resides in the provision of an improved drive mechanism interposed between parallel spaced crankshafts to drive a centrally disposed propeller shaft.

Another object of the invention is to provide an aircraft engine having two parallel crankshafts operated from banks of cylinder units and a centrally disposed propeller shaft wherein improved gear mechanism is provided for driving the propeller shaft from the cram-shafts.

A further object of the invention is to provide an aircraft engine of the foregoing character in which a shock absorbing drive is interposed between thecrankshafts and the propeller shaft.

Another object of the invention is to provide an aircraft engine having spaced parallel crankshafts and a reduction gear drive between the crankshafts and the propeller shaft having incorporated therein flexible or resilient coupling means eflective during operation of the engine a) absorb shocks and damp out torsional vibraons.

Still a further object of the invention is to provide a gear drive between a plurality of crankshafts and a propeller shaft in which torsionalvibrations are neutralized or materially reduced.

Another object of the invention is to provide a reduction gear drive between corresponding ends of a pair of crankshafts and the propeller shafts and gear interconnections between opposite corresponding ends of the crankshafts thereby improving the distribution of forces on the crankshafts, materially reducing torsional vibrations, and effecting a better balance of the crankshafts.

A further object of the invention is to provide an aircraft engine of the dual crankshaft type in which the rear ends of -the crankshafts have a non-positive driving connection between each other.

Also it is an object of the invention to provide a dual crankshaft aircraft engine having a positive driving connection between the forward ends of the crankshafts and a non-positive driving connection between the crankshafts and the propeller shaft.

More specifically it is an object of the invention to provide a dual crankshaft aircraft engine in which the reduction gear drive between the forward endsof the crankshafts and the propeller shaft embodies a resilient coupling, and in which a gear connection is provided between the rear ends of the crankshafts which also embodies a resilient coupling.

In the operation of aircraft, it is desirable that all of the elements of the craft be proportioned and streamlined in such a manner as to pass through. the air with the minimum resistance, and if possible to cooperate with other elements of the craft to produce lift. As the necessity for larger and faster aircraft'increases, the problem of developing more powerful engines with decreased resistance or drag presents increasing diiliculties. An object of this invention is to provide a more powerful engine having less frontal area capable of producing resistance or drag than has heretofore been possible.

A further object of the invention resides in the provision of spaced engine units having angularly inclined power units disposed in novel nesting relation adjacent each other to provide a power-- ful engine having the minimum frontal area.

A still further object of the invention is to position a pair of engine units each having cylinder units disposed at an angle of approximately in such an improved manner that the outer ends of the cylinders of each engine 'unit lie adjacent each other, thereby minimizing the front area of the engine.

,Another object is to provide an engine having angularly inclined generally oppositely disposed groups of cylinder units having their outer ends positioned adjacent each other, wherein a combustible mixture is supplied to all of the cylinders at oppositely disposed points adjacent their outer ends, and the products of combustion are discharged outwardly from the cylinders at points approximately opposite the inlet points.

' Other objects and advantages of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of 'this specification wherein like reference characters designate corresponding parts in the several views.

Fig. l is a. side elevation, partly broken away, of an airplane embodying the present inventi n. Fig. 2 is a side elevation of the engine mounted within the airplane disclosed in Fig. 1.

Fig. 3 is a front end elevation of the engine illustrated in Fig. 2.

perspective the gear drive between the crankshafts and the propeller shaft.

Fig. 7 is a section. partly diagrammatic, taken substantially through lines |'l of Fig. looking in the direction of the arrows. v

Fig. 8 is a section, partly diagrammatic, taken substantially through lines ll of Fig. 5 looking in the direction of the arrows.

Before explaining in detail the present invention it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in'various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation, and it is not intended to limit the invention claimed herein beyond the requirements of the prior art.

For the purpose of illustrating the present invention there is shown, by way of example, in the drawings a mult'i-cylinder internal combustion plates as and 40a. As illustrated in Fig. 5,-the front ends or portions of the housings I8, 44 and 42 may be closed by means of a concavo-convex streamlined'end plate 43 rigidly secured in position. The crankcase housing 38 receives the inner ends of the generally upwardly and downwardly extending cylinder units 44 and 4| of two vertically spaced banks of cylinders and in like manner the crankcase housing 40 receives the inner ends of similarly arranged cylinder units 44 and 41 of the other two vertically spaced banks of cylinders. The cylinders are preferably so arranged that the included angle between the upwardly and downwardly extending cylinders on each side, i. e. cylinders 44 and 45 on one side and cylinders 48 and 41 on the opposite-side, is approximately 135, thereby giving equal firing intervals during the operation of the engine and providing a very compact construction occupyinga minimum of space.

Referring to Fig. 4, it will be noted that the cylinders 44 and 45 are provided with pistons 48 operably connected to the crankshaft 32 through engine together with the drive mechanism between the crankshafts of the power plant and the propeller shaft installed within a suitable airplane iillustrated in Fig. 1. This airplane comprises a fuselage l4 including a passenger compartment ll, generally laterally extending wings I! and an empennage to assist in controlling the direction of flight of the craft. A streamlined engine compartment 22 houses the power plant 24 which in turn is adapted to drive a propeller 28 to propel the craft through the air.

In the present instance the power plant of the airplane comprises an engine of the double v-' type, as clearly illustrated in Figs. 2 to 4 inclusive. This engine is provided with oppositely inclined banks of cylinders disposed in such a manner that the outer ends of generally upwardly and downwardly extending cylinders of spaced cylinder groups or banks are positioned to lie adjacent each other. It will be observedthat the engine thus formed is generally oval in shape. Thus, in the present embodiment of the invention there are illustrated four banks or groups of engine units or cylinders arranged angularly with respect to one another, each bank or group comprising a suitable number of cylinders such as eight in the present instance. The illustrated engine, therefore, comprises thirty-two cylinders although it will be understood that a different number may be utilized. It will thus be seen from the construction of the power plant that the engine as a whole is particularly adapted for use in a wing structure wherein it may be laid on its side, or it may be mounted upright as a central power plant as illustrated in Fig. 1. When mounted in either position it may be readily surrounded by a streamlined shell whereby frictional resistance to the air is minimized.

,Referring particularly to Figs. it and 5, it will be seen that a centrally disposed propeller shaft 30 adapted to receive the propeller 26 is driven by spaced parallel right and left crankshafts 32 and 34, respectively, through improved reduction gear mechanism designated as a whole at 34. The crankshafts 32 and 34 are rotatably Journaled at their rear ends through the medium of suitable bearings 3i and 31 in crankcase housings II and 40, respectively, these housings being separated by a central truss-like housing 42. The crankcase housings 38 and 40 are accessible at their outer sides by means of convex cover the medium of connecting rods 49 and 50, respectively. In like manner the cylinders 46 and 4'! are provided with pistons operably connected to the crank shaft 34 by-means of similar connecting rods 5| and 52 respectively. The adjacently arranged connecting rods 48 and 50 and in like manner the adjacently arranged connecting rods SI and 52 are provided, respectively, with bearings 54 and 58 adapted to surround offset cranks of the crankshaftslfl and 34, and are securely fixed thereto by means of caps 58 having threaded extensions 60 adapted to project through spaced apertures in the flared larger ends of the connectingrods to receive nuts 62 to maintain the parts in assembled relation. By positioning the parts in the manner illustrated more desirable distribution of weight is effected because of a reduction in the radius of gyration of rod and crank assembly. Better balance resulting in less vibration and more uniform operation of the engine are, therefore, achieved.

As illustrated in Fig. 2, the upper and lower cylinder units 44 and 45, or 46 and 41, of each of the vertically spaced units are offset slightly longitudinally relative to each other whereby the connecting rods 49 and 50, or 5| and 52,. connecting the opposed upper'and lower pistons of the cylinder units may be mounted side by side on single crank arms of the crankshafts. A more rugged and economical crankshaft design is, therefore, possible and greater simplicity of bearing construction for the two crankshafts is achieved.

Each cylinder may be supplied with'a combustible mixture through the use of suitable fuel injectorsinot show'n) of any known type. Air may be supplied to the cylinders throughv the medium of manifold passageways 10, I2, 14 and 16 formedin the central housing 42, see Fig. 4,

these passageways communicating by means of supercharger on each side of the engine. It

will be noted that the supply of combustible mixture is from the inner side of each cylinder outwardly towards the cylinder, and the exhaust outer sides of the cylinders.

\ In the present instance the intake of the com bustible mixture into each cylinder, also the scavenging and exhaust of the products of com bustion, are controlled by valve mechanism positioned in the outer extremities of the cylinders. The intake passage for each cylinder and the exhaust passage 86 communicate with inlet and outlet ports in a rotary cone-type valve 81 mounted in the cylinder head. Each valve as seen in Fig. 4 has an outwardly projecting stub shaft 88 Journaled'through the medium of suit= able bearings in the cylinder head. Each shaft 88 carries a bevel gear as in mesh with a gear 9i secured to a valve driving shaft 90. Each valve actuating shaft 90, together with gearing 89 and 9!, operates in a longitudinally extending housing 92. v The valve mechanism may be constructed in accordance with my application Serial No. 192,602. The shafts 90 arepreferably hollow to minimize weight and to permit the flow of oil therethrough for lubricating purposes. The inner face of the rotary valve s1 is concave to cooperate with the complementary convex head 48a of the piston, the valve having an interior dome-like combustion chamber 81a with which the intake and exhaust passages 18 and 86 communicate at. intervals during. rotation of the valve. The'spark plug for each cylinder also communicates with the, combustion chamber or cavity at predetermined intervals duringthe rotation of the valve for the purpose of firing the compressed mixture.

The valve actuating shafts $6 for the upper and lower banks of cylinders at each side of the power plant are driven from the crankshafts 32 and 34 by suitable mechanism such as illustrated in my application Serial No. 296,836. Such mechanism may also in part be utilized to operate the distributor mechanism, as in said application. The valve actuating shaft housings 92 at the lower extremity of the engine at the rear thereof are preferably interconnected at Ma, as

'shown in Fig. 3, to permit lubricating oil to flow from one of the housings 92 to the other during operation of the engine. An oil pump or pumps may be positioned in either or both housings at 93 to circulate oil to the vital parts of the engine needing lubrication. These pumps may be driven from the adjacent valve actuating shafts. The oil pump mechanism may be constructed in accordance with my above mentioned application Serial No. 296,836..

In theevent that the front end of the engine is lower than'the rear end, as when the craft is diving, oil will be transmitted through the hol-' low valve actuating shafts ill from the opposite end of the engine by the suctionlcreated by the oil pumps. If it is desired to fly the craft in inverted position for sustained periods of time, the upper housings 92 may be interconnected and one or more oil pumps positioned to be driven by the valve actuating shaft in the manner above referred to in connection with the pumps located at points 93 in Fig. 3.

Rbferring particularly to Figs. to 8 inclusive within the crankcase housings 38 and II for the four banks of cylinders or engine units is located shafts and the propeller shaft 10.

Rigldly secured to the forward ends 61' the crankshafts 32 and 34 are gears 94 and 95 respectively. The gear 84 meshes with a larger gear 98 fixed to a short shaft 97 journaled in bearing bosses 98 and 99 extending from the crankcase housing 38. These bosses also provide bearings for the front end of the crankshaft 32. In like manner, the gear 95 meshes with a gear MB, similar to gear 96, fixed to a short shaft IBI, similar'to shaft 91, journaled in bearing bosse's I62 and H33 extended from the opposite crankcase housing so. These bosses also pro-. vide bearings for the front end of the crankshaft 34. Secured to the shaft 91 forwardly of the gear 86 isa relatively small gear I04 and correspondingly secured to the shaft Ilii is a gear Hi5 similar to the gear I04. The reduction gears I04 and I05 mesh with a single .plane compound gear I08 fixedto the hollow propeller shaft 38. The gear I06, in the present instance, 'is constructed to provide a flexible coupling between the crankshafts and the propellershaft. For the purposes of exempliflcation of this feature of the invention the gear I06 comprises an outer gear ring I051; and an inner hub member lliib fastened on the propeller shaft. Interposed between the annular hub lush and the outer gear ring I061: is a resilient coupling ring which in the present instance is formed of elastic rubber material which may be bondedto the adjacent faces of the hub member IIIGb and the gear ring Into so that torsional vibrations may be absorbed through the inner internal friction of the rubber. The foregoing construction of the driven gear I06 of the reduction gear mecha- I nism, providing a resilient coupling between the crankshafts and the propeller shaft thereby in-" v terrupting the metallic path, is a present preferred construction, it being understood that in propeller 26 to the propeller shaft, the latter is,

journaledin suitable -bearings I98 in the forward end of the concavo-convex end plate 31 attached to the crankcase housings. It should be understood that, although there is a resilient coupling between the crankshafts and the propeller shaft,

there is a solid or direct positive drive between.

the two crank'shafts through the medium of gear ring Ilia meshing with gears I and I",

In accordance with the foregoing I have described the present preferred reduction gear v drive between the spaced parallel crankshafts 32.

1 uand the centrally located propeller shaft ll.

I will now describe the present preferred manner in which the crankshafts are interconnected at the mechanism for driving the propeller shaft 30 the'rear end of the power plant, reference in this respect being had to Figs. 5 to 8 inclusive,

The connection between the rear ends of the crankshafts is in the form of gearing having incorporated therein a flexible coupling interposed between the crankshafts. Rigidly secured to the crankshaft 02 adjacent its rear end and intermediate the bearing bosses I! is a gear H0. In like manner, a similar gear III is fixed to the crankshaft 34 at its rear end intermediate the bearing bosses 01. It will be noted that the gears III and III are not coplanar, the gear III being oifset somewhat rearwardly of the gear IIO. These'gears mesh with separate exterior teeth formed on a dual plane compound gear I I2. This compound gear comprises a main gear member Ill having teeth meshing with the teeth of gear IIO,'and also comprises a second gear member II4 spaced rearwardly of the gear member I I3 and having external teeth meshing with the gear III. Gear member I It may be freely mounted through the medium of a resilient rubber bushing on an extended hub portion Inc of the gear H3. Interposed between the faces of gear members H3 and lil is a resilient rubber disk II! which is either bonded to the opposed faces of the gear members or clamped tightly so that relative torsional vibrations of the crankshafts are absorbed principally through internal friction of the rubher, there preferably being little or no skin friction at the opposite faces of the rubber disk. It will be seen from the foregoing that the resilient rubber couplings I01 and ilainterrupt the metallic path between the crank kpafts and also between the latter and the propeller shaft. A driv-. ing circuit is thus completed between the banks of connecting rods of the cylinders and the two crankshafts through opposite ends of these shafts. the propeller shaft being connected in this circuit and being relatively free of torsional vibrations to which the crankshafts may be subjected.

By interconnecting the crankshafts in the above described manner it may be said that the front one-half of each crankshaft is coupled at gear I06a direct or positively to the other, whereas the remaining rear halves of the crankshafts are flexibly or resiliently connected together. This construction will overcome the torsional vibrations of the crankshafts to such an extent as to reduce by substantially or nearly one-half the torsional vibrations, an important factor owing to the length of the crankshafts.

The gear member N3 of the compound gear II! is keyed through the medium of its hub Ilia to a short shaft I I0 Journaled in suitable bearings III in bosses projecting from the crankcase housings. The crankshafts 32 and 04 are provided with rearward shaft extensions I I0 which may be utilized for the purposes of accessory drives, such as to drive machine gear synchronizing mechanisms and other necessary elements. A pair of oppositely disposed generators II! interposed between pairs of distributors I20 at the forward end of the power plant may be driven through the medium of drive shafts I2I actuated from the crankshafts. The shafts III, as shown in Fig. 5, have worm drive connections with shafts I22 operatively connected to the distributors.

The power plant may be positioned within the streamlined shell 22 in such a manner that air is directed between the cylinders and flows outwardly between the cylinders and over the heat radiating and rigidifying fins on the cylinders to cool the engine. If desired the cylinders may be jacketed and cooled with liquid.

Referring to Figs. 6 and 7, it will be noted that idler gears 96 and I00 are located at opposite sides of an imaginary line passing through the centers of the crankshafts 02 and 34 and the propeller shaft 30. In these figures the assumed direction of rotation of the propeller shaft and crankshafts and the associated gearing is indicated by thearrows. Thus, 'it will be seen that gear is located at the one side (below in Fig. '1) of this crankshaft centerline which lies furthest therefrom in the direction of rotation of the propeller and crankshafts. In like manner, the gear I00 is located at the opposite side (above in Fig. 7) of this centerline and furthest therefrom in the direction of rotation of the propeller and crankshafts. By thus locating the gear unit 90. I04 and the gear unit I00, III! in the manner shown at opposite sides of the centerline of the crankshafts with respect to the directions of rotation thereof and of thepropeller shaft, the loads on the bearings for these gears are materially reduced, By virtue of this construction, therefore, it is possible not only to reduce the size of the bearings but also the idler gears, resulting in a much more compact, efflcient and durable transmission.

' An important feature of the present invention resides in the manner in which the transmission gearing is assembled and the resilient couplings pre-loaded. After assembling the crankshafts and propeller shaft with the gearing associated therewith in meshing relation at the forward and rear ends of the crankshafts, either one of the crankshafts is turned in its bearings relatively to the other crankshaft a predetermined amount, such as one or more degrees, thereby placing a torsional load on the resilient couplings and taking up the slack between the meshing gears. As a result of this relation between the gearing of the respective crankshafts, and as a result of. the preloading of the resilient couplings I01 and II, a much more eflioient and quieter operating engine is obtained and improved damping of torsional vibrations is achieved. Thus, if it is considered that the engine consists of two flat sixteen cylinder engines set oneagainst the other, it will be clear that the power output at the propeller shaft is equal to that of a thirty-two cylinder engine. In this connection the banks of cylinder units 44 and 45 together with associated parts may be considered as one V-type sixteen cylinder engine and the opposite banks of cylinder units 40 and 41 may be considered the other V-typesixteen cylinder engine, these engines being arranged in opposed relation and operable to drive a single centrally disposed propeller shaft. In order to hold these engines in step in relation to each other, they normally would be timedas a thirty-two cylinder engine. Back lash in the gears is overcome by the above described manner in which the two engines are connected together, i'.e., overlapping preventin with an internal combustion engine for driving a propeller shaft comprising a pair of substantially parallel crankshafts, a propeller shaft extendng generally parallel to the crankshafts in a plane therebetween, a reduction gear drive between corresponding ends of said crankshafts and the propeller shaft, and a non-positive resilient driving connection independent of the propeller shaft between the opposite corresponding ends of the crankshafts.

2. Gearing means to be used in connection with an internal combustion engine for driving a propeller shaft comprising a pair of substantially parallel crankshafts, a propeller shaft extending generally parallel to the crankshafts in a plane therebetween, driving means between corresponding ends of the crankshafts and the propeller shaft, and a non-positive driving connection independent of the propeller shalt between the opposite ends of the crankshafts.

3. Gearing means to be used in connection with an aircraft internal combustion engine for driving a propeller shaft comprising a pair oi substantially parallel crankshafts, a propeller shaft, gearing for driving said propeller shaft from the crankshaits, and non-metallic means for preloading the teeth of said gearing.

4. Gearing means to be used in connection with an aircraft internal combustion engine for driving a propeller shaft comprising a pair or substantially parallel crankshafts, a propeller shaft, gearing for driving said propeller shaft irorn the crankshaft-s, and torsionally stressed means for preloading the teeth of said gearing.

5. Gearing means to be used in connection with an aircraft internal combustion engine for driving a propeller shaft comprising a pair at substantially parallel crankshafis, a propeller shaft, gearing for driving said propeller shait from the crankshafts, and a resilient coupling interposed in said searins and torslonally stressed when the engine is at rest to load said gearing, said resilient coupling being adapted to interrupt the metallic path between said crankshafts and propeller shaft.

8. Gearing means for driving a propeller shaft comprising a pair of substantially parallel crankshai'ts, a propeller shalt extending generally parallel to the crankshafts' in a plane therebetween, a reduction gear drive between corresponding ends of said crankshafts and the propelier shaft, and a non-metallic non-positive driving connection between the opposite corresponding ends of the crankshafts. V

7. Gearing means for driving a propeller shaft comprising a pair of substantially parallel cranksheits, a propeller shaft extending generally parallel to the cranlsshafts in a plane therebetween, driving means between corresponding ends of the crankshaits and. the propeller shaft, and a non-metallic non-positive driving connection between the opposite ends or the crankshafts.

8. Gearing means for use in connection with an internal combustion engine for driving a propeller shaft, comprising a pair of substantaliy parallel cranhshafts, gear mechanism between the forward ends of the .crankshafts and said propeller shaft, an idler shaft interposed between Ziii the crankshafts rearwardly of the propeller shaft and independent of the latter, a compound gear having one part secured to said. idler shaft and another part yieldinglv connected to said one part, and gear means connecting each crankshaft with one of said parts of the compound sear.

an internal combustion engine for driving a pro peller shaft, comprising a pair of substantially gear, said yielding connection comprising a ruleher coupling adapted to be torsionally stressed.

com: Tums.

Gearing means for use inconnection with 

